1. Field of the Invention
In general, the present invention relates to a magnetoresistive sensor mounted on a magnetic recording/reproducing apparatus or another magnetic detecting apparatus. In particular, the present invention relates to a magnetoresistive sensor and its manufacturing method, wherein the magnetoresistive sensor is of the so-called spin-valve type, and wherein the electrical resistance thereof varies due to a change in relation between the direction of the magnetization of a pinned magnetic layer and the direction of magnetization of a free magnetic layer which is affected by an external magnetic field.
2. Description of the Related Art
FIG. 3 is a diagram showing a front view of a magnetoresistive sensor based on the spin-valve effect disclosed in U.S. Pat. No. 5,206,590. The Z direction in the figure is the moving direction of a magnetic recording medium such as a rigid disk relative to the magnetoresistive sensor whereas the Y direction is the direction of a leaking magnetic field (an external magnetic field) from the magnetic recording medium.
In the magnetoresistive sensor shown in FIG. 3, a nonmagnetic underlayer 2 made of a nonmagnetic material such as Ta (tantalum) is created on a lower-gap layer 1 made of typically Al.sub.2 O.sub.3 (aluminum oxide). A free magnetic layer 3 is created on the nonmagnetic underlayer 2. A nonmagnetic electrically conductive layer 5, a pinned magnetic layer 6 and a second antiferromagnetic layer 7 are stacked on the free magnetic layer 3 with a predetermined width in the X direction one after another in the order they are enumerated. At (i) portions on both edges of the nonmagnetic electrically conductive material 5 and the pinned magnetic material 6, first antiferromagnetic layers 4 are created on the free magnetic layer 3.
An upper layer 8 made of a nonmagnetic material such as Ta is created on the first antiferromagnetic layers 4 on both the sides and on the second antiferromagnetic layer 7 in the middle. Lead layers (electrically conductive layers) 9 are created on the upper layer 8, sandwiching an open track width Tw.
An exchange anisotropic coupling on a film boundary surface between the first antiferromagnetic layer 4 and the free magnetic layer 3 puts the free magnetic layer 3 into a single-domain state in the X direction, orientating the directions of magnetization in the X direction. On the other hand, an exchange anisotropic coupling on a film boundary surface between the second antiferromagnetic layer 7 and the pinned magnetic layer 6 puts the pinned magnetic layer 6 into a single-domain state in the Y direction, fixing the directions of magnetization in the Y direction (a direction perpendicular to the surface of the paper toward the reader).
In the magnetoresistive sensor based on the spin-valve effect, a steady-state current is supplied from the lead layer 9 to the free magnetic layer 3, the nonmagnetic electrically conductive layer 5 and the pinned magnetic layer 6 in the X direction. When a leaking magnetic field (an external magnetic field) from a magnetic recording medium such as a rigid disk is provided in the Y direction, the direction of magnetization of the free magnetic layer 3 changes from the X direction to the Y direction. The change in relation between the direction of magnetization in the free magnetic layer 3 and the pinned direction of magnetization of the pinned magnetic layer 6, which change is caused by a variation in magnetization direction in the free magnetic layer 3, changes the electrical resistance. The change in electrical resistance results in a change in voltage which is used for detecting the leaking magnetic field from the magnetic recording medium.
As described above, in the magnetoresistive sensor shown in FIG. 3, the exchange anisotropic couplings on the film boundary surface between the first antiferromagnetic layer 4 and the free magnetic layer 3 and on the film boundary surface between the second antiferromagnetic field 7 and the pinned magnetic layer 6 orientate the magnetic directions of the free magnetic layer 3 and the pinned magnetic layer 6 respectively in directions perpendicular to each other. As a result, the amount of Barkhausen noise can be reduced, giving rise to a merit that a linear response characteristic of the change in electrical resistance with respect to the leaking magnetic field from the magnetic recording medium can be reliably obtained. In addition, since the dimension of the pinned magnetic layer 6 in the X direction is fixed, the off-track performance with respect to the magnetic recording medium is also good.
In a process of manufacturing a magnetoresistive sensor with a structure shown in FIG. 3, however, after the nonmagnetic electrically conductive layer 5, the pinned magnetic layer 6 and the second antiferromagnetic layer 7 are formed on the free magnetic layer 3 using sputter processes, it is necessary to remove the nonmagnetic electrically conductive layer 5, the pinned magnetic layer 6 and the second antiferromagnetic layer 7 from the (i) portions using an etching process such as ion milling. In addition, also required is a process for creating the first antiferromagnetic layer 4 on the (i) portions at both edges of the second antiferromagnetic layer 7, the pinned magnetic layer 6 and the nonmagnetic electrically conductive layer 5 each with a fixed dimension in the X direction.
The film thickness of each layer in the magnetoresistive sensor has a value ranging from several tens of Angstroms to several hundreds of Angstroms. The film thickness of the nonmagnetic electrically conductive layer 5 is about several tens of Angstroms. It is extremely difficult to remove the stacked structure comprising the three layers, that is, the nonmagnetic electrically conductive layer 5, the pinned magnetic layer 6 and the second antiferromagnetic layer 7, each having such a very small film thickness by means of ion milling with a high degree of accuracy. From the technological point of view, at the portion (i), it is also difficult to remove only the nonmagnetic electrically conductive layer 5 without removing the free magnetic layer 3 in order to expose the free magnetic layer 3. If a portion of the free magnetic layer 3 is inadvertently removed in this etching process, the magnetic characteristic of the free magnetic layer 3 will be adversely affected. If the nonmagnetic electrically conductive layer 5 is inadvertently left at the portion (i) on the surface of the free magnetic layer 3, on the other hand, the first antiferromagnetic layer 4 created on the free magnetic layer 3 is not closely adhered to the free magnetic layer 3 because of the residual nonmagnetic electrically conductive layer 5. As a result, no exchange anisotropic coupling is generated on the film boundary surface between the first antiferromagnetic layer 4 and the free magnetic layer 3.